Method for transmitting data in the access area

ABSTRACT

In state of the art baseband methods, the range in the access area decreases with increasing transmission speed. When a limit is reached with a predetermined distance and a selected speed, it is no longer possible to change over to an even greater speed. Otherwise, the synchronism between the transmitter and receiver is lost. The invention resolves this deficiency by combining the features of broadband technology with an acknowledged message exchange by means of which the parameters can be controlled between the transmitter and the receiver.

[0001] The invention relates to a method according to the preamble of claim 1.

[0002] In the access area, data are supplied to one or more subscribers (receiving devices) from a transmitting device. The transmitting device can be constructed as a multiplexer or, in the case of telephony, as a local exchange. In this arrangement, different transmission methods are applicable.

[0003] When state of the art baseband methods are used, the range decreases with increasing transmission rate. This means that when the transmission rate is increased, the data to be transmitted can only be supplied to subscribers via trunk lines of ever decreasing length. If, with a predetermined distance and a selected rate, the limit is already reached, it is no longer possible to switch to an even higher rate. Since the distance to the limit is often unknown, one possibility of solving the problem consists in changing the rate in small steps. However, this frequently results in performance being given away. As an alternative, in principle, only those ranges can be selected at which it is ensured that they can be bridged even at the maximum possible rate.

[0004] If the transmission rate between the transmitting device and the receiving devices is to be increased, this can only be done in such a manner that both stations (i.e. transmitting device and receiving devices) operate at the same increased rate. For this purpose, the receiving device in question in each case must be informed by one of the stations such as, e.g. the transmitting device, that an increase in transmission rate is required and corresponding setting instructions must also be transmitted for this purpose.

[0005] The communication between transmitting device and receiving device required for this purpose takes place via a separate channel. This can be designed as independent outband channel (user data and control data (signaling data) are conducted via different links) or inband channel (user data and control data are conducted via one link). In the latter case, care must be taken, with appropriate reliability of range, that the communication between the two stations is still ensured after switching up to a higher rate. In cases of doubt, therefore, the rate for an existing connection must be maintained.

[0006] Increasing the transmission rate above the critical limit presents problems in as much as the level arriving at the receiving site is too low in this case and, in consequence, synchronism between the transmitting device and the receiving device is lost (“receiving device disconnecting”) and thus communication between the two stations is no longer possible. The reason for this is that in this case, the transmitting device has already adjusted itself to the increased rate but the remote station is still operating at the old rate by itself.

[0007] Communication is then no longer possible since the remote station is “disconnected”. Interworking is only possible again when both stations are manually set to the same rate.

[0008] The invention is based on the object of indicating an approach to how synchronism between transmitting and receiving device can be reliably achieved again even after the transmission rate has been changed.

[0009] On the basis of the preamble of claim 1, the invention is attained by the features specified in the characterizing clause.

[0010] The advantageous factor in the invention is the use of an acknowledged message exchange between the master device (local station) and the slave devices (remote stations). To this extent, this combines the characteristics of broadband technology with an acknowledgement. This is associated with the advantage that the remote stations are not disconnected since otherwise they could no longer be reached. Due to the fact that synchronism is achieved time and again, the blocking probability of the system is reduced.

[0011] Advantageous further developments of the invention are provided in the subclaims.

[0012] In the text which follows, the invention is explained in greater detail with reference to an exemplary embodiment shown in the FIGURE.

[0013] The FIGURE shows a configuration with a local station M and a plurality of remote stations S₁ . . . S_(n). The local station M can act as a master device (transmitting device) and the remote stations S₁ . . . S_(n) can act as slave devices (receiving devices). According to the invention, an acknowledged message exchange is carried out between master device M and slave devices S₁ . . . S_(n).

[0014] In the present case, it is assumed that the transmission of user data between the master device M and the slave devices S₁ . . . S_(n) is to be controlled at an increased transmission rate v_(new). This process is initiated by the master device M. Communication between the master and the slave device takes place via an inband channel. To obtain a better understanding, only the increase in transmission rate between the master device M and only one of the slave devices S₁ . . . S_(n), e.g. S₁, is described.

[0015] Firstly, a message N is transmitted to the slave device S₁ via a management channel, by means of which message it is informed that the transmission rate v_(old) previously used is to be increased. The message N is still transmitted at the old transmission rate v_(old) so that the slave device S₁ can receive the message N without problems. At the same time, a timer T_(M) is started in the master device M, on the one hand, and, on the other hand, the corresponding adjustments for increasing the transmission rate v_(old) to the new transmission rate v_(new) are carried out.

[0016] The message N is received and evaluated by the slave device S₁. In response, the corresponding adjustments for increasing the transmission rate v_(old) are carried out in the slave device S₁. This process is acknowledged, already at the new increased transmission rate v_(new), by means of an acknowledgement message via the management channel to the master device M. At the same time, a timer T_(S) is also started in the slave device S₁.

[0017] The acknowledgement message is evaluated by the master device M and, depending on the result of the evaluation, a further acknowledgement message is supplied to the slave device S₁. Once the slave device S₁ has received its message, it can assume that the master device M is also capable of transmitting at the new increased transmission rate v_(new). It is only when the slave device S₁ has received this acknowledgement message at the new transmission rate v_(new) that the transmission link for transmitting the user data at the new, increased transmission rate v_(new) is released. If an incorrect action takes place during these processes, the timers T_(M), T_(S) ensure, after a predetermined timeout period, that both stations switch back to the old transmission rate v_(old). If necessary, the switchover can then be started again by the master device M.

[0018] In the present exemplary embodiment it has been assumed that only the increase in transmission rate between master device M and slave device S₁ is controlled. The relevant information is deposited in the message N. However, the invention is not restricted to this type of message exchange. Thus, a multiplicity of other parameters can be exchanged. Examples of this are parameters such as clock characteristic, clock variants in master/slave, state characteristics (master/slave), synchronous/asynchronous operation or CRC check. Since the slave devices can become “disconnected” in the prior art, these parameters must often be transmitted in the correct order.

[0019] In a further embodiment of the invention, it is then provided for arbitrarily varying this order of the parameters to be changed to the slave device. This is a direct consequence of the invention according to which the timeout period prevents the remote station from becoming “disconnected”. It provides the possibility for automatic transmission rate detection and utilization of a maximum possible transmission rate with a predetermined line length.

[0020] In the latter case, the process begins at a low transmission rate at which it is ensured that the range can be bridged by the system. The transmission rate is then increased step by step until neither of the two acknowledgement messages can be received any more. The user data are then transmitted at the transmission rate at which the acknowledgement was still successfully carried out last.

[0021] This is associated with the advantage that in the case of a new installation of a connection, the transmission link can be automatically adjusted optimally with regard to transmission rate and line length. The prerequisite for this in each case is a station previously defined as master device or slave device with the lowest rate as the default setting. When autoconfiguration is activated, the master then automatically then begins to change the rate once the synchronization has been established at the lowest rate. 

What is claimed is:
 1. A method for changing the transmission rate in an access area, including a transmitting device and at least one receiving device which operation in a master/slave configuration, the transmitting device being designed as master device and the receiving device being designed as slave device, comprising: exchanging messages between the master device and the at least one slave device; sending a message with a first transmission rate to the slave device; acknowledging, via the slave device, based on a result of an evaluation of the received message, the reception of the message to the master device with the aid of a first acknowledgement message transmitted at a second transmission rate; acknowledging, via the master device, the reception of the first acknowledgement message to the slave device with the aid of a second acknowledgement message transmitted at the second transmission rate; and resuming the original state when one of the two acknowledgement messages does not arrive within a predetermined period of time.
 2. The method as claimed in claim 1, wherein the message has information about whether the transmission rate and/or other parameters are to be changed.
 3. The method as claimed in claim 1, wherein the parameters are clock variants in the master/slave synchronous/asynchronous operating mode or data transmissions with or without CRC error corrections.
 4. The method as claimed in claim 1, wherein the first transmission rate is lower than the second transmission rate.
 5. The method as claimed in claim 1, wherein the message is transmitted via a management channel together with the user channel.
 6. The method as claimed in claim 1, wherein beginning at a low transmission rate, the rate is increased step by step until the first or second acknowledgement message can no longer be received whereupon the user data are transmitted at the transmission rate at which the two acknowledgement messages were still received successfully last. 